1. Technical Field
The present invention relates to a nucleic acid extracting or dispensing device.
2. Related Art
In the biochemical field, techniques of PCR (polymerase chain reaction) have been established. In recent years, amplification accuracy and detection sensitivity in the PCR method have been improved, and thus an extremely trace amount of specimen (such as DNA) can be amplified, detected, and analyzed. PCR is a method of applying thermal cycling to a solution (reaction solution) containing a nucleic acid as an amplification target (target nucleic acid) and a reagent to thereby amplify the target nucleic acid. As the thermal cycling of PCR, a method of applying thermal cycling at temperatures of two stages or three stages is usually adopted.
On the other hand, for the diagnosis of infectious diseases such as influenza at the site of medical care, the use of rapid test kits of immunochromatography and the like is the mainstream under the present circumstances. In such rapid tests, however, accuracy is sometimes insufficient, so that it is desired to apply PCR, from which higher test accuracy can be expected, to the diagnosis of infectious diseases. Moreover, in a general outpatient practice or the like in medical institutions, since the examination time is limited, the time that can be spent for a test is limited to a short time. Therefore, the reality is that a test for influenza, for example, is performed by a simple test such as immunochromatography, at the expense of test accuracy, for shortening the time.
Because of such circumstances, for realizing a test by PCR, from which higher accuracy can be expected, at the site of medical care, the time required for the reaction needs to be shortened. As an apparatus for performing PCR reaction in a short time, JP-A-2009-136250, for example, discloses a biological sample reaction apparatus that rotates a biological sample reaction chip filled with a reaction solution and a liquid that is not miscible with the reaction solution and has a specific gravity smaller than that of the reaction solution, about an axis of rotation in a horizontal direction to thereby move the reaction solution for applying thermal cycling. Moreover, as methods of PCR, a method of using magnetic beads (JP-A-2009-207459), a method of performing thermal cycling of PCR by moving a droplet in a temperature change region on a substrate using magnetic beads as moving means of the droplet (JP-A-2008-012490), and the like are disclosed.
Further, since specimens and reagents used for PCR are often rare and expensive, it is preferable that the amount (volume) of a reaction solution of PCR is smaller in view of cost and efficiency. Hence, a method that can handle the reaction solution of PCR in as small an amount as possible is desired. As an example of a method of handling a trace amount of liquid, JP-A-2004-025148 discloses a method of transferring a target liquid through a narrow tube using a sending liquid that is not miscible with the target liquid but is separable in phase therefrom. Moreover, JP-A-2007-175002 discloses, as a gene analyzing apparatus, an apparatus that performs PCR by moving a reaction solution of PCR within a channel, and a method of using the apparatus.
As described above, studies for shortening the time required for the thermal cycling of PCR are underway. However, the situation is that a technique for shortening the time required for extracting a nucleic acid serving as a template from a specimen to establish a state where PCR can be initiated has not been sufficiently developed. For example, for performing PCR, treatment (hereinafter sometimes simply referred to as “pretreatment”) of extracting a nucleic acid (DNA (deoxyribonucleic acid) and/or RNA (ribonucleic acid)) serving as a template from a specimen (such as blood, nasal mucus, or oral mucosa) is needed. Even if the time required for the thermal cycling of PCR can be shortened, when the time required for extracting the nucleic acid (pretreatment) cannot be shortened, it is impossible to sufficiently meet demands at the site of medical care.
Although pretreatment using a column or magnetic beads is usually performed, all of the dispensing, stirring and centrifugal work, and the like of a reagent are manually performed, or an expensive and large-scale apparatus such as an automatic extraction apparatus is needed. Then, even in any of the methods, the time and effort for at least 30 minutes or more are required for the pretreatment. Hence, even if only the thermal cycling of PCR can be performed in a short time (for example, within 15 minutes), the reality is that at least about one hour is required for the overall test time from the collection of a specimen to a result of the test when the time required for the pretreatment is added.
Hence, it is realistically difficult, at the site with restrictions such as clinic hours, to consistently perform the test from the nucleic acid extraction (pretreatment) to the thermal cycling of PCR. Such a circumstance is one of obstacles for the widespread use of the test method using PCR in medical institutions. That is, the time and complication required for PCR itself and pretreatment are causes that make it difficult for the test method using PCR to come into widespread use at the site of medical care, in spite of the fact that PCR is a test method with higher sensitivity and higher accuracy than immunochromatography.
Moreover, in the method disclosed in the related art document, the volume of the target liquid to be handled is larger than 0.5 μL (microliter). Therefore, the target liquid itself is prepared separately on a larger scale. Hence, preparation of the target liquid can be performed using, for example, instrument or an experimental tool available on the market. However, with improvement in microreaction techniques and increasing demand for cost reduction in PCR, preparation of the target liquid of a volume about 1 μL is required. In such a case, an exact volume of solution containing a specimen and a reagent in orders of nanoliter (nL) (less than 1 μL) needs to be handled for measurement, sending, or the like. However, in the dispensing method in the related art, it is difficult to precisely handle a trace amount of liquid. For example, even when a manually operated pipette, which is perceived to be relatively precise, is used, it is difficult to measure, send, and dispense, with good accuracy, a liquid whose volume is as small as less than 0.2 μL.